1. Field of the Invention
This invention relates in general to disk drives, and in particular to use of specific molecular weight oils for lubricating the coil wire during the winding of coils which are used in disk drive components in order subsequently to reduce the occurrence of stiction during operation of the disk drive and improve drive performance.
2. Description of Related Art
Moving magnetic storage devices, especially magnetic disk drives, are the memory device of choice. This is due to their expanded non-volatile memory storage capability combined with a relatively low cost.
Magnetic disk drives are information storage devices which utilize at least one rotatable magnetic media disk having concentric data tracks defined for storing data, a magnetic recording head or transducer for reading data from and/or writing data to the various data tracks, a slider for supporting the transducer adjacent the data tracks typically in a flying mode above the storage media, a suspension assembly for resiliently supporting the slider and the transducer over the data tracks, and a positioning actuator coupled to the transducer/slider/suspension combination for moving the transducer across the media to the desired data track and maintaining the transducer over the data track center line during a read or a write operation. The transducer is attached to or is formed integrally with the slider which supports the transducer above the data surface of the storage disk by a cushion of air, referred to as an air bearing, generated by the rotating disk.
Alternatively, the transducer may operate in contact with the surface of the disk. Thus the suspension provides desired slider loading and dimensional stability between the slider and an actuator arm which couples the transducer/slider/suspension assembly to the actuator. The actuator positions the transducer over the correct track according to the data desired on a read operation or to the correct track for placement of the data during a write operation. The actuator is controlled to position the transducer over the desired data track by shifting the combination assembly across the surface of the disk in a direction generally transverse to the data tracks. The actuator may include a single arm extending from a pivot point, or alternatively a plurality of arms arranged in a comb-like fashion extending from a pivot point. A rotary voice coil motor (vcm) is attached to the rear portion of the actuator arm or arms to power movement of the actuator over the disks.
The vcm located at the rear portion of the actuator arm is comprised of a top plate spaced above a bottom plate with a magnet or pair of magnets therebetween. The vcm further includes an electrically conductive coil disposed within the rearward extension of the actuator arm and between the top and bottom plates, while overlying the magnet in a plane parallel to the magnet. In operation, current passes through the coil and interacts with the magnetic field of the magnet so as to rotate the actuator arm around its pivot and thus position the transducer as desired.
The magnetic media disk or disks in the disk drive are mounted to a spindle. The spindle is attached to a spindle motor which rotates the spindle and the disks to provide read/write access to the various portions on the concentric tracks on the disks. The spindle motor contains conductive coils in the spindle motor windings.
These electrically conductive coils are typically wound from an insulated wire. The wire may, in addition, have a bond coat to help facilitate the shaping or forming of the coil. In either case, a film of oil coating is often applied to keep the wire from sticking to itself prior to winding of the wire into a coil. When the wire is wound into the coil, oil may be trapped between and/or in the layers of winding as well as being found on the outer surfaces of the coil. As power is supplied to the coil during operation, the coil becomes hot and the oil coating in and on the coil volatilizes to generate a vapor inside the drive. The vapor migrates from the actuator or spindle motor assembly and condenses upon the surface of the disk where the temperature is significantly cooler than in the actuator or spindle motor assembly. This presents problems for normal operation of the disk drive because this vapor phase transport provides means for the lubricant to exit the coil and contaminate the disk drive.
To accommodate the current capacity requirements of disk drives as well as meeting the size constraints of laptop or notebook markets, disks are being stacked very closely together with the expectation they can be written to and read from within these very small spacings. Accordingly, extremely smooth surfaces exist on both the disk surface and the magnetic recording face of the slider attached to the load arm of the actuator. These extremely smooth surfaces are necessary to support the low fly height associated with high density recording. However, with the condensation of the lubricant coating from the coil onto the disk surface, the surface becomes chemically contaminated, causing the problem of stiction in the drive. Stiction occurs as two very smooth surfaces stick to each other and effectively prevent the removal of one from the other. The stiction forces may be sufficient to prevent the rotation of the disk; but if the disk can be rotated, damage almost certainly will occur to the surface of the disk or slider due to the fact that the slider is in contact with and stuck to the disk surface as the disk moves relative to the slider.
One approach considered in addressing the problem of stiction has been to use a higher resistance coil, or to adjust coil performance by continually checking the temperature or a temperature estimation and not driving the coil at temperatures which would cause outgassing of the lubricant. These approaches however are problematic in that they negatively effect the performance of the drive. For example, seek rates in the actuator would be affected by lowering the performance of the coil, or desired higher RPMs of the spindle motor might not be obtainable by limiting the coil temperature.
It therefore can be seen that there is a need for providing a coil wire for use in disk drive components such as the actuator assembly or spindle motor which is free of lubricants that will outgas during operation and contaminate the surface of the disks in the drive.
Another consideration in coil selection is the manufacturability of the coil. One common method of coil winding involves unspooling of the wire off one end of a non-rotating flanged spool, through a series of tensioner pulleys onto a spinning mandrel. The wire stops and starts moving rapidly, and is heated just before arriving at the mandrel using a hot air jet. The temperature at this point could exceed 450 degrees Celsius. The dimensional requirements and number of turns and layers of the coil, and precise stacking of the wire on itself place high demands on the wire quality, frictional characteristics and bond coat performance. It can therefore be further seen that there is a need to provide a conductive coil for a hard disk drive wherein the oils used to lubricate the wires that create the coil maintain low friction in the spooling, despooling and coiling winding operations. It can also be seen that there is a need to eliminate the problems of stiction in operating a disk drive assembly.
To overcome the limitations of the background art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses an improved coil wire and method of manufacturing coil assemblies which are adapted for use in hard disk drives. It is one aspect of the invention to provide an improved coil for use in an actuator assembly that is free of the molecular weight hydrocarbon range based lubricants which contribute to stiction problems during disk drive operation. It is a further object of the invention to provide conductive wire coil assemblies for use in various disk drive components, such as spindle motor windings, having lubricants that will not contribute to stiction problems in operation of the disk drive. It is a further object of the invention to provide an improved coil wire that will maintain low friction in the spooling, despooling and coil winding operations.
In order to accomplish the objects of the present invention, in a preferred embodiment a coil assembly is provided wherein a high molecular weight hydrocarbon based lubricant is used to coat the coil wire in the assembly. The coil wire is comprised of an electrical conductor enclosed by an insulating layer. An adhesive bond coat may overlay the insulating layer to aid in the forming and shaping of the coil. A lubricant layer overlies either the insulator or alternatively the bond coat to prevent the coil wire from sticking to itself during the spooling and despooling operations prior to coil winding. The preferred embodiment is a lubricant which experiences less than or equal to 10% weight loss at 2 to 2xc2xd times the operating temperature of the coil in degrees Celsius. In one embodiment, the lubricant is preferably a high molecular weight hydrocarbon based lubricant having molecular weight of greater than or equal to 700.
In operation of the disk drive, as power is supplied to the coil, the coil becomes hot. However, due to the high molecular weight of the lubricant selected, the oil does not volatilize but rather remains intact as a coating on the coil.
In an alternative embodiment, a very low molecular weight hydrocarbon based lubricant is used to coat the coil wire in the coil assembly. The coil wire is comprised of an electrical conductor enclosed by an insulating layer. An adhesive bond coat may overlay the insulating layer to aid in the forming and shaping of the coil. A lubricant layer overlies the bond coat to prevent the coil wire from sticking to itself during the spooling and despooling operations prior to coil winding. The lubricant is alternatively a low molecular weight hydrocarbon based lubricant having a molecular weight of 226. In operation of the disk drive, current passes through the coil and the coil becomes hot. In this alternative embodiment, the oil comprising the lubricant layer of the coil has either been completely volatilized in the manufacturing process or any residual material will be completely volatilized and thus there is no subsequent condensation on the surface of the disk, and therefore, no contamination.
Although the preferred embodiment of the present invention is shown and described in connection with the coil found in the actuator assembly, it will be appreciated by those skilled in the art that the wire coils and methods of manufacturing the same described herein are also applicable to other coil windings found within a disk drive, such as within the spindle motors, solenoids, etc. Additionally, the results obtained have been achieved by correction of the stiction problems of a specific head/disk interface. Those skilled in the art would appreciate that adjusting the molecular weights of the lubricant for different interfaces or for different operational results could be done without departing from the spirit or scope of the invention.
These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and form a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to accompanying descriptive matter, in which there is illustrated and described specific examples of an apparatus in accordance with the invention.